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Breslow Intermediates from a Thiazolin‐2‐ylidene and Fluorinated Aldehydes: XRD and Solution‐Phase NMR Spectroscopic Characterization
Author(s) -
Paul Mathias,
Neudörfl JörgM.,
Berkessel Albrecht
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201904308
Subject(s) - chemistry , dimer , substituent , nuclear magnetic resonance spectroscopy , protonation , medicinal chemistry , aldehyde , photochemistry , stereochemistry , organic chemistry , catalysis , ion
Abstract The first generation and X‐ray diffraction (XRD) analysis of a crystalline Breslow intermediate (BI) derived from a thiazolin‐2‐ylidene, that is, the aromatic heterocycle present in vitamin B 1 , is reported. Key to success was the combined use of pentafluorobenzaldehyde and a thiazolin‐2‐ylidene carrying an enol‐stabilizing dispersion energy donor as N‐substituent. A so‐called primary intermediate (PI) could be isolated in protonated form (pPI) as well and analyzed by XRD. Furthermore, the first stable BI derived from an aromatic thiazolin‐2‐ylidene and an aliphatic aldehyde (trifluoroacetaldehyde) was prepared and characterized by NMR spectroscopy in solution. When switching to a saturated thiazolidin‐2‐ylidene, reaction with pentafluorobenzaldehyde afforded a new BI in solution (NMR spectroscopy). Attempts to crystallize the latter BI resulted in the isolation of a novel thiazolidin‐2‐ylidene dimer that had undergone rearrangement to a hexahydro[1,4]‐thiazino[3,2‐b]‐1,4‐thiazine.